Print hammer positioning means employing high velocity gas stream directed against hammer



United States Patent O 3,279,361 PRINT HAMMER PGSITIONING MEANS EMPLOY- ING HIGH VELOCITY GAS STREAM DIRECTED AGAINST HAMMER Leo J. Emeuaker, Playa Del Rey, Calif., assguor to Data Products Corporation, Culver City, Calif., a corporation of Delaware Filed Jau. 4, 1965, Ser. No. 423,276 13 Claims. (Cl. 101-93) This invention relates generally to high speed printing apparatus and more par-ticularly to hammer assemblies for use therein.

High speed printing devices utilizing rotating printing drums are well known in the prior art. Typically, such drums have alphabetic and/ or numeric print-ing characters on the surface thereof arranged in columnar fashion. More particularly, the drum is provided with a plurality of circumferen-tial tracks equal to the maximum number of characters to be printed on any one line and each such track includes one full set of characters which the particular printing device is adapted to print.

In such printing devices, a hammer assembly is associated with each circumferential track and includes a hammer or impact device which can be caused to strike a selected character during the rotation of the drum in response to appropriate control signals. An inked ribbon and a paper strip upon which data is to be printed are usually positioned between the drum and the hammers. Each hammer, when actuated, thus strikes the back of the paper strip thereby forcing the paper strip against the ribbon, and the ribbon in turn against the character on the drum to consequently print the selected character on the front of the paper strip.

Typical prior art hammer assemblies consist of a movable impact device which is associated with a solenoid such that upon energization of the solenoid coil, a solenoid armature is driven against the impact device to thereby propel it against the paper. In attempting to significantly increase the speed of printing devices, problems arise involving the coupling between the solenoid armature and the impact device and in an effort to solve these problems, improved hammer assemblies have been introduced, as for example disclosed in U.S. Patent Number 3,087,421. The hammer assembly disclosed in the cited patent avoids coupling problems by mounting a coil directly on the impact device and associating the coil with a stationary magnetic field such that energization of the coil develops a magnetic field which interacts with the stationary magnetic field to thus propel the impact device against the paper strip.

In hammer assemblies employing the basic concept of mounting a magnetic field generating means on a movable impact device for interacting with a stationary magnetic field, the movable field generating means is usually positioned in a gap defined by a stationary field generating means. Thus, where an energizable coil is carried by the impact device, it is usually positioned in a gap defined between a pair of permanent magnets. Since it is desired that as great a magnetic field as possible be available in the gap, the gap is usually made very narrow. Consequently, unless the impact device is very precisely positioned, the coil will often rub against one of the permanent magnets on either side of the gap. The resulting friction will cause the impact device travel .time to vary thus causing misalignment of the printed characters. Accordingly, it has been the practice to very carefully position the impact device by, for example, providing V-shaped positioning receptacles for receiving the impact device supports and constructing the supports so as to restrain movement in a lateral direction while permitting easy movement both toward and away from the printing drum in a longitudinal direction.

In view of the above, it is an object of the present invention to provide means for automatically positioning a device within a gap so that it does not contact the sides thereof.

It is an additional object of the present invention to provide hammer assemblies in which impact devices thereof can be less expensively and more accurately positioned within a defined gap.

Briefiy, the present invention is based on .the recognition that a device received between a pair of closely spaced side walls can be initially positioned and maintained in spaced relationship to each side wall by a fluid ejected from one of the side walls.

In accordance with a preferred embodiment of the present invention, an impact device coil is received in a gap defined by space-d magnet surfaces. Air is projected at a high speed into the gap from an opening formed in one of the magnet -surfaces and its velocity results in a reduction in air pressure between the coil and the magnet surface (Bernoullis principle). Thus, the normal air pressure on the opposite coil surface drives the coil laterally towards the air projecting surface. As the coil moves closer toward the air opening, the air velocity of course decreases thereby permitting the pressure to increase. Thus, the coil will come to s-ome stable lateral position, spaced from the air projecting surface by a thin layer of air. The coil will thus lock in some stable lateral position without the use of any structural support means which might restrict its longitudinal movement.

A related positioning problem encountered in high speed printing devices involves the longitudinal rest position of each impact device. That is, in order for the printed characters to be aligned, it is necessary that the travel time of each impact device be the same so that all of the printing characters are struck in the same relative angular position of the drum. In order to equalize the travel times of the plurality of impact devices, .adjustable mecha-nical backstop means are usually provided which establish the rest position for each impact device. Due to each impact device repeatedly colliding against its backstop, the backstop eventually wears thereby requiring adjustment. In order to avoid this problem. it is a further object of the present invention to provide impact device backstops which are not subject to wear.

Accordingly, an ancillary feature of the present invention involves providing an adjustable screw backstop defining an air opening therein. By permitting the proper amount of air at the right velocity to exit from the opening, a reduced pressure region can be developed to hold the impact device adjacent the adjustable screw but spaced by a thin air layer therefrom. The air jet escaping from the adjustable screw also functions to absorb some of the impact device rebound energy and thus to reduce its velocity prior to the Bernoulli effect fixing its rest position. As a consequence of this velocity reduction, backstop wear is virtually eliminated completely. In addition to facilitating the deceleration of the impact device, the air jet will aid its forward acceleration after the hold of the Bernoulli effect is broken, thus improving the efficiency of the apparatus.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its organization and method of operation, as well as additional objects and Aadvantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is a sectional view through a high speed printing apparatus illustrating hammer assemblies constructed in accordance with the present invention;

FIGURE 2 is a horizontal sectional view taken substantially along the plane'2-2 of FIGURE 1;

FIGURE 3 is a vertical section View taken substantially along the plane 3-3 of FIGURE l; and 7 FIGURE 4 is an enlarged vertical sectional view taken through the backstop assembly.

Attention is now called to FIGURE 1 which illustrates a portion of a high speed printing apparatus including a printing surface 10 in the form of a rotatable drum which defines a plurality of tracks, each track including a set of characters adapted to be printed by the apparatus. Positioned adjacent the drum is a paper strip 12 and interposed therebetween is a printing ribbon 14.

As is well known in the art, the paper strip 12 is incrementally moved in a vertical direction, line by line, relative to the center line 11 of the printing drum. A plurality of hammer assemblies are provided each having -an impact device 16 positioned in alignment with a diiferent track and the center line of the drum adjacent the rear surface of the paper strip 12. Each of the impact devices 16 is adapted to be propelled in a longitudinal direction such that it strikes the back of the paper strip 12 to urge it against the ribbon 14 and drum 10. The character thus struck on the drum 10 will cause a printed impression to be formed on the front surface of the paper 'strip 12. Inasmuch as a full set of characters is contained in each drum track, any one of these characters can be printed at a horizontal position in a line by causing the impact device 16 in alignment with that position to strike the paper strip when the selected character is in alignment with the drum center line.

As previously noted, many techniques have been utilized to propel an impact device for printing purposes. One very useful arrangement involves providing a selectively energizable magnetic eld generating means on the impact device 16 which, when energized, functions to develop a magnetic field which interacts with a stationary magnetic iield to thus propel the impact device 16 longitudinally.

Although various magnetic iield generating coniigurations have been suggested, a preferred embodiment involves providing a coil assembly 18 on each impact device'16, which coil assembly includes a coil 20 contained within a coil housing 22. Preferably, in order to develop balancing forces on the impact 16, the coil assembly 18 symmetrically projects above and below the impact device 16. Of course, non-symmetric coil assembly configurations could be utilized with appropriate balance compensation being provided in the impact device itself. The coil 20 can be formed of a very small electrical conductor so that the housing 22 can be thin and flat. The ends of the conductor forming the coil 20 preferably extended through channels (not shown) formed in the underside of the impact device 16 and terminate in recesses 24 and 26. In the recesses, the coil ends are connected, as by soldering, to flexible conductive support members 28 and 30. The support members 28 and 30 respectively extend through insulated sleeves 32 and 34 which are retained in a base 36. The lower ends of the support members 28 and 30 project below the base 36 and are available for connection to a current source (not shown) which can selectively supply current to the coil 20 to thus develop -a magnetic field extending in a lateral direction transverse to the longitudinal axis of the impact device 16.

In order to develop a propelling force on the impact device 16, a stationary magnetic iield is provided for interacting with the magnetic field selectively generated by the coil 20. The stationary magnetic field adjacent each coil is preferably formed by a pair of spaced permanent magnets, as 38 and 40, which have parallel opposed walls defining a gap 42 therebetween. In order to print closely spaced characters, e.g. on 1/10 inch centers, it is of course necessary that the impact devices 16 be correspondingly spaced adjacent the strip. In order to achieve this close spacing, it is desirable to reduce as much as possible the thickness ofthe magnets 33 and 40 and the gaps 42 therebetween. Inasmuch as it is usually not possible to space the impact devices so closely in a single tier, it is common practice to provide two or more tiers of hammer assemblies With the impact devices of each tier being interleaved. A realistic figure for the gap thickness is on the order of .G40-.050 inch and for the housing 22 thickness .030 inch. It Will thus be seen that the clearance between the housing 22 and the magnet side walls can be on the order of .O10 of an inch. Inasmuch as it is imperative that the coil housing 22 sit in the gap Without rubbing against either of the side Walls, since such rubbing would significantly affect the travel time of the impact device, it has been necessary in the past to exercise extreme care in positioning the impact device during' assembly of the apparatus. In view of this, cost of assembling a printing apparatus of this type has in the past been Very high. In addition to requiring extreme care in assembly, means had to be provided for maintaining the lateral position of each impact device, once established. Consequently, the conductive support members 2S and 30 were often formed of at iiexible members which displayed very little compliance in lateral direction.

In accordance with the invention, in order to reduce assembly and maintenance costs of a printing apparatus of the aforedescribed type, means are provided for automatically positioning the coil assembly `=22 Within the gap 42. More particularly, in accordance with the invention, an opening 44 is de-ined in one magnet wall adjacent each gap 42. The opening 44 communicates with a passage 46 which in turn is in communication with a mani'- fold 48. In order to position the coil housing 22 within the gap so that it is not in contact with either of the side walls, air is forced through the manifold 48 and out through the holes 44. As a consequence of the Bernoulli effect, the air exiting into the gap from the opening 44 creates a reduced air pressure region between the magnet side Wall containing the opening 44 and the surface of the coil housing 22 adjacent thereto. Consequently, the coil housing 22 is in elect sucked toward the magnet side wall containing the opening 44. As the coil housing 22 moves closer to the magnet side Wall, the velocity of the air exiting from the opening 44 Will thus be reduced to thereby increase the pressure so that the coil housing is established in an equilibrium position spaced from the magnet wall containing the opening 44 by a very thin layer of air. Accordingly, without requiring high assembly costs, assurance is had that none of the coil housings 22 Will rub against the magnet side Walls.

Only one opening 44 has been illustrated for each gap 42 because it has been experimentally found that this will suiiice for the materials and apparatus dimensions tested. Of course however, more than one opening canbe used without departing from the contemplation of the invention. Inasmuch as the opening 44 need be defined on only one side of each gap 42, the passages 46 only have to be provided in every other magnet. Although an opening 44 has been shown as being defined in only one gap side Wall, each side wall could have an opening if desired in order to permit the impact device to be drawn toward and spaced from either Wall. Such an arrangement may be advantageous in environments Where the apparatus is subjected to extreme shock and vibration.

A related positioning problem which arises in high speed printing apparatus of the aforedescribed type involves the establishment of the longitudinal rest position of each impact device 16. That is, since it is desired that all of the impact devices 16 strike the characters on the drum in the same relative position, it is necessary that all of the impact devices sta-rt from the same relative rest position, assuming that they are all subjected to the same external forces. In previous printing apparatus, adjustable backstops have been provided which function to establish the rest position of the impact device and in addition function to absorb a portion of the energy with which each impact device rebounds from the drum. In accordance with the present invention, a backstop assembly 60 is provided which includes a block 62 defining an internally threaded opening 64 in alignment with each of the impact devices 16. An externally threaded screw element 66 is received in each opening 64 so that the screw 66 can be moved longitudinally toward and away from the impact device with which it is aligned. Each screw element 66 defines an opening 68 formed in a front surface 70 positioned opposite the rear end surface of an impact device 16. The opening 68 communicates through a channel 71 with a manifold 72 through a passage 74. In order to position the impact devices 16, air is supplied to the manifold 72 and exits through the opening 68 at a high velocity to thus create a Bernoulli effect between the rear end surface of the impact device 16 and the front surface 70 of the screw element 66. Thus, the impact devices 16 are sucked toward the surfaces 70. The screw elements 66 are adjustably supported so that minor variations in the forces applicable to each impact device can be compensated for by adjusting the rest position of the impact device. In addition to establishing the rest position of the impact device, the air exiting from the opening 68 functions as a cushion to absorb some of the impact device rebound energy and thus decelerate the impact device to rest without additional rebounding. In addition to facilitating deceleration, forward acceleration is facilitated by the air exiting from opening 68 thus reducing the requirements of the coil drivers (not shown).

From the foregoing, it should be appreciated that an improved apparatus has been disclosed herein for positioning impact devices in a printing apparatus relative to a magnet gap and a printing surface. Several advantages are offered by apparatus constructed in accordance with the present invention over prior art designs. Initially, considerable economy is introduced in the fabrication of the apparatus inasmuch as various surfaces need not be fabricated to as close a tolerance as has previously been required. In addition, other apparatus previously utilized to position the impact devices is not required. Considerable time and labor is also saved introducing still further economies. Secondly, the conductive members 28 and 30 can comprise round springs being compliant in both directions rather than the more expensive fiat springs previously used to assure non-compliance in a lateral direction. Maintenance problems are also reduced inasmuch as round springs having a uniformly smooth surface generally have a greater exural fatigue resistance than fiat springs which often have minute edge cracks which ultimately break under continued use. The utilization yof round springs of course permits a reduction in spring width which facilitates the close packaging of the sleeves 32 and 34.

Thirdly, and very significantly, due to the fact that the coil housings are effectively automatically aligned within the permanent magnet gaps, a smaller gap width can be utilized thus making available a greater fiux density wit-hin the gap. Thus, a reduced coil current is required for a given driving force. This of course improves hammer efficiency and more significantly, reduces the heat generated in the coil and the demands yon the current drivers and power supply. Moreover, not only is there a reduction in the amount of heat generated, but because the gap width is reduced, the thermal resistance of the path from the coil to the hammers is reduced thereby providing more effective cooling. Further, the fact that the air is expanding after it exits from the various openings inherently provides an additional cooling effect.

Fourthly, it has been found that the air flow within the banks of hammer assemblies effectively flushes dirt, paper dust, etc. from the gap thus further reducing hammer drag. In addition, the air flow within the gap establishes a greater lateral stiffness than is afforded by flat spring conductors previously used to support the impact devices. As a consequence, a printing apparatus constructed in accordance with the present invention functions better than prior apparatus in environments where it is subjected to shock and vibration.

Although a particular type of impact device has been shown herein, it should be appreciated that the invention is applicable in any situation where a member is to be positioned in a gap in spaced relation to the side walls. Further, although air has been referred to throughout the foregoing description, it should further be appreciated that various other fluids can be employed.

What is claimed is:

1. In a printing apparatus including a pair of spaced parallel side Walls defining an elongated gap therebetween; at least one fiexible member having first and second ends; means fixedly securing said first end relative to said side walls; a fiat impact member mounted on said second end and at least partially disposed in said gap, said member having first and second side surfaces extending parallel to said side walls and first and second end surfaces extending lateral to said side walls; first and second means for respectively establishing the lateral and longitudinal position of said member; said first means including at least one opening in a first of said side walls; means for ejecting high velocity gas through said opening into said gap to thus develop a low pressure region between said first side wall and one of said side surfaces; said second means including an element defining an aperture therein positioned opposite to said first end surface and means for ejecting high velocity gas through said aperture to thus develop a low pressure region between said first end surface and said element.

2. The combination of claim 1 wherein said element is mounted for adjustable longitudinal movement.

3. In a printing structure, apparatus for positioning an impact device having a first surface and mounted on at least one flexible support member for movement in a direction extending perpendicular to said first surface, said apparatus comprising a wall defining an opening therein positioned opposite to said first surface; and means for ejecting high velocity gas through said opening to thus develop a low pressure region between said first surface and said wall.

4. The structure of claim 3 wherein said first surface is an end surface and said wall is mounted for adjustable longitudinal movement.

5. The structure of claim 3 wherein said impact device comprises a fiat elongated impact device and said first surface is a side surface thereof.

6. A high speed printing apparatus including a printing surface and plurality of hammer assemblies, each of said hammer assemblies comprising first means including spaced parallel first and second walls defining a gap therebetween and including means for providing a magnetic field across said gap; an elongated impact device mounted for longitudinal movement relative to said first means; a magnetic field generating means carried by said impact device for providing a magnetic field adapted to interact with said magnetic field in said gap to develop a force for propelling said impact device against said printing surface; said magnetic field generating means including a portion disposed in said gap having a surface extending parallel to said first wall; means for positioning said magnetic field generating means portion in said gap including an opening defined in said first wall; and means for ejecting high velocity gas through said opening into said gap to thus develop a low pressure region between said first wall and said surface.

7. The apparatus of claim 6 wherein said first means includes first and second spaced permanent magnets having opposed walls comprising said first and second walls; and wherein said magnetic field generating means includes a coil carried by said impact device.

8. The apparatus of claim 7 including iirst and second flexible support members adapted to ilex in both a lateral and a longitudinal direction.

9. The apparatus of claim 8 wherein said first and second support members are conductive and said coil includes first and second terminals respectively connected thereto.

10. The apparatus of claim 6 including a plurality of backstops each positioned in alignment with one of said impact devices; each of said backstops including an element defining an aperture therein; and means for ejecting high velocity gas through said apertures and against said impact devices to thus reduce the velocity with which said impact devices rebound from said printing surface and to provide a low pressure region between said impact devices and said elements for positioning said impact devices when they are at rest.

11. The apparatus of claim 10 including a mounting block having a plurality of threaded receptacles therein and wherein each of said elements is threadedly received in one of said receptacles for movement toward and away from said printing surface.

12. In a high speed printing apparatus including a printing surface and a plurality of impact devices means for selectively applying a force to each of said impact devices for propelling it against said printing surface; a plurality of backstops each positioned in alignment with one of said impact devices remote from said printing surface;

each of said backstops includingan element defining an aperture therein; and means for ejecting high velocity gas through said apertures and against said impact devices to thus reduce the velocity with which said impact devices rebound from said printing surface and to provide a low pressure region between said impact devices and said elements for positioning said impact devices when they are at rest.

13. The apparatus of claim 12 including a mounting block having a plurality of threaded receptacles therein and wherein each of said elements is threadedly received in one of said receptacles for movement toward and away from said printing surface.

References Cited by the Examiner UNITED STATES PATENTS 2,953,371 9/1960 Smith 271-26 3,087,421 4/1963 Irwin et al. 101-93 3,122,039 2/ 1964 Sowers lOl-93 X 3,126,200 3/ 1964 Rehm 271-26 3,149,562 9/1964 Wilkins et al. 101-93 3,168,307 2/ 1965 Walton et al. 271-26 3,172,352 3/1965 Helms 101-93 3,172,353 3/1965 Helms 101-93 ROBERT E. PULFREY, Primary Examiner.

E. S. BURR, Assistant Examiner. 

1. IN A PRINTING APPARATUS INCLUDING A PAIR OF SPACED PARALLEL SIDE WALLS DEFINING AN ELONGATED GAP THEREBETWEEN; AT LEAST ONE FLEXIBLE MEMBER HAVING FIRST AND SECOND ENDS; MEANS FIXEDLY SECURING SAID FIRST END RELATIVE TO SAID SIDE WALLS; A FLAT IMPACT MEMBER MOUNTED ON SAID SECOND END AND AT LEAST PARTIALLY DISPOSED IN SAID GAP, SAID MEMBER HAVING FIRST AND SECOND SIDE SURFACES EXTENDING PARALLEL TO SAID SIDE WALLS AND FIRST AND SECOND END SURFACES EXTENDING LATERAL TO SAID SIDE WALLS; FIRST AND SECOND MEANS FOR RESPECTIVELY ESTABLISHING THE LATERAL AND LONGITUDINAL POSITION OF SAID MEMBER; SAID FIRST MEANS INCLUDING AT LEAST ONE OPENING IN SAID FIRST OF SAID SIDE WALLS; MEANS FOR EJECTING HIGH VELOCITY GAS THROUGH SAID OPENING INTO SAID GAP TO THUS DEVELOP A LOW PRESSURE REGION BETWEEN SAID FIRST SIDE WALL AND ONE OF SAID SURFACES; SAID SECOND MEANS INCLUDING AN ELEMENT DEFINING AN APERTURE THEREIN POSITIONED OPPOSITE TO SAID FIRST END SURFACES; AND MEANS FOR EJECTING HIGH VELOCITY GAS THROUGH SAID APERTURE TO THUS DEVELOP A LOW PRESSURE REGION BETWEEN SAID FIRST END SURFACE AND SAID ELEMENT. 